| Author | Message | | | eric | | Posted: Sun Aug 27, 2006 11:09 am Post subject: LED Voltage Tester | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | B. Kainka
A universal voltage tester should respond to both dc and ac
voltages. The usual types with glow-discharge lamps only
work with voltages greater than around 100 V. The circuit
shown in Figure 1 uses a Darlington circuit formed by two
NPN transistors and can detect voltages of less than 1 V. It can
also be used to test continuity. Here the positive terminal of
the battery serves as the ‘ground’ connection. Consequently,
an input current flows even with a high-impedance connection,
but this current increases when a voltage source with the
proper polarisation is included in the loop. A supplementary
piezoelectric buzzer allows the circuit
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